1. Field of the Invention
The invention relates to an internal combustion engine in which chain covers are secured to a cylinder head with a fastening bolt.
2. Description of Related Art
Japanese Patent Application Publication No. 2012-137044 (JP 2012-137044 A) describes an example of an internal combustion engine in which a chain cover is secured to a cylinder head with a fastening bolt. In such an internal combustion engine, a chain that transmits the rotation of a crankshaft to camshafts is disposed in a space defined between the cylinder head and the chain cover.
In some internal combustion engines, a first chain cover and a second chain cover are secured to a cylinder head with a fastening bolt. For example, the first chain cover is attached to the cylinder head, and the second chain cover is attached to the first chain cover. A chain is disposed in a space defined between the first chain cover and the second chain cover.
In such an internal combustion engine, a liquid gasket, such as a formed-in-place gasket (FIPG), may be provided between the first chain cover and the cylinder head.
More specifically, the first chain cover is provided with a cutout so as to avoid contact with camshafts that project from the cylinder head in their axial direction. Due to the cutout provided in the first chain cover in the above-described manner, a portion of the peripheral edge of the first chain cover is positioned between a crankshaft and the camshafts. The portion of the peripheral edge of the first chain cover, the portion being positioned between the crankshaft and the camshafts, will be referred to as “specific edge portion”. A flange is provided at the specific edge portion of the first chain cover. Further, a flange is provided at a portion of the cylinder head, the portion facing the specific edge portion. The liquid gasket is interposed between these flanges. The liquid gasket is brought into close contact with these flanges. As a result, the sealing performance of an area between the flanges is enhanced.
When the chain covers are secured to the cylinder head with the fastening bolt, edge portions of the peripheral edge of the first chain cover other than the edge portion formed due to the provision of the cutout in the first chain cover are pressed toward the cylinder head by the peripheral edge of the second chain cover, but the specific edge portion of the first chain cover is not pressed toward the cylinder head by the second chain cover. Thus, a force with which the liquid gasket is held by the flanges is not so large. This makes it difficult to enhance the degree of close contact between the flanges and the liquid gasket. Thus, it is difficult to enhance the sealing performance of the area between the flanges.
In order to enhance the sealing performance of the area between the flanges, it is desirable to provide a boss through which a shaft portion of the fastening bolt is passed, near each of the flanges. Thus, an axial force generated by tightening the fastening bolt is transmitted to the liquid gasket. This increases the force with which the liquid gasket is held by the flanges. As a result, the degree of close contact between the liquid gasket and the flanges is enhanced, leading to enhancement in sealing performance of the area between the flanges.
Next, steps of securing each of the chain covers to the cylinder head will be described. In a first step, an uncured liquid gasket is applied to at least one of the flange of the first chain cover and the flange of the cylinder head, and the first chain cover is attached to the cylinder head. In a second step, a chain is looped over the crankshaft and the camshafts. In a third step, the second chain cover is attached to the first chain cover. In a fourth step, the chain covers are secured to the cylinder head by tightening the fastening bolt.